1. The Field of the Invention
The present invention relates to structures for electrically connecting an integrated circuit to external circuitry. More particularly, the present invention relates to interposer structures having formed thereon a plurality of conductive pillars or recesses that are adapted to make electrical contact with the leads of an integrated circuit package.
2. The Relevant Technology
Frequently, after an integrated circuit is manufactured, a testing process is conducted on the integrated circuit by subjecting it to a preselected set of input conditions in order to measure its response or other parameters. Such testing is often conducted on a chip package that includes an integrated circuit. As used herein, the terms xe2x80x9cintegrated circuit packagexe2x80x9d and xe2x80x9cchip packagexe2x80x9d refer to an assembly that includes an integrated circuit or another semiconductor structure in combination with external and additional structure. The term xe2x80x9csemiconductor structurexe2x80x9d extends to any device or assembly that includes circuitry defined in a semiconductive material, and further extends to a chip package that includes semiconductive material. The external and additional structure of a package assembly may be used, for example, for mounting the semiconductor structure to a printed circuit board or other external circuitry, for establishing electrical connection between the semiconductor structure and external circuitry, for improving the ease of handling or transporting the semiconductor structure, and/or for protecting the semiconductor structure from environmental conditions.
Many chip packages include a lead frame that extends beyond the body thereof. The lead frame typically includes an array of electrical leads that extend from the internal circuitry of the integrated circuit to the exterior portion of the chip package where they are exposed to the surroundings. Testing of an integrated circuit package that includes a lead frame assembly is conventionally conducted by providing temporary electrical communication between the leads and testing circuitry. For example, such temporary electrical connection may be established by using a set of probes, pins, sockets, or the like, to contact the leads. The integrated circuit package may be clamped or otherwise secured in position during the testing operation in order for the leads to remain in electrical contact with the corresponding probes, pins, sockets, etc., of the testing circuitry.
Regardless of which electrical connection technique is employed, it is desirable to effect a connection that causes as little damage as possible to be leads. If the temporary connection to contact surfaces damages the leads, the entire integrated circuit package may be rendered useless.
The trend in the semiconductor manufacturing industry is towards smaller devices and an increase in the number of leads connected to an integrated circuit package. This has the result of reducing the distance between nearest leads on an integrated circuit package. In particular, the pitch of leads, which is defined as the distance between corresponding points on nearest adjacent leads, has progressively grown smaller.
As the pitch of integrated circuit packages decreases, it becomes ever more difficult to effectively and reliably establish temporary electrical contact with the leads without damaging the leads. The difficulties are compounded in light of the fact that testing is generally more reliable when electrical contact is made with leads as near to the body of the integrated circuit package as possible. If contact is instead made with the leads a relatively large distance from the body of the integrated circuit package, the resulting long conductive segments of the leads can generate considerable interference and noise which may disrupt the testing procedure.
Establishing electrical connection with leads near the body of integrated circuit package is further desirable as integrated circuits operate at ever higher speeds. If electrical connection is established at a relatively great distance from the body of a high-speed integrated circuit package, signals are not able to be received and transmitted at the proper synchronization or at the proper timing, which may cause the integrated circuit to malfunction or the testing procedure to become disrupted.
It can be easily understood that the factors that encourage electrical connection to be established relatively near the body of the integrated circuit package are often in conflict with efforts for making contact with conventional fine pitch lead frames. The probes, sockets and the like that have been used in the prior art are often not able to adequately balance these considerations and increasingly are unable to provide reliable electrical connection for conducting testing procedures.
Accordingly, it can be appreciated that it would be an advancement in the art to provide an interconnect structure that can provide electrical connection with leads near the body of an integrated circuit package, particularly when the leads have a relatively fine pitch.
The present invention relates to interposer structures that include a plurality of contact structures formed thereon in a pattern that corresponds to electrical leads of an integrated circuit package. The contact structures are arrayed across a surface of the interposer structure in a position so as to make electrical connection with the leads of an integrated circuit package when the integrated circuit package is positioned thereover. The contact structures include a conductive layer for electrically engaging the leads and an electrical trace having a first end in contact with the conductive layer and an opposite second end configured to be connected with another conductive structure. For example, wire bonded leads, conductive tape or non-bonded leads may be connected with the second end of the traces. These wires or leads in turn terminate at terminal contact points that preferably have a pitch greater than the pitch of the leads of the integrated circuit package. In this manner, relatively fine pitch leads can be connected to conventional sockets or other mounting structures on a testing device that have a greater pitch by means of the interposer structure.
The interposer structures of the invention include a dielectric or a semiconductor substrate over which the contact structures may be formed. The semiconductor substrate is preferably substantially composed of silicon or a silicon containing material. Alternatively, a dielectrics substrate can be formed over a semiconductor substrate. The dielectric substrate may be disposed over a body portion of the interposer structure or may instead be an integral portion of the interposer structure.
Under a first embodiment of the invention, an array of raised members are formed on the dielectric or semiconductor substrate, with each raised member having a top surface distal to the dielectric or semiconductor substrate. A conductive layer is deposited or otherwise formed on the top surface of each of the raised members. The raised members are sized and spaced so that the conductive layers formed thereover may electrically engage the leads of an integrated circuit package. The raised members may be formed from the dielectric or semiconductor substrate using any suitable etching procedure or other micromachining operation. Silicon or silicon containing material is a preferred material for use in the dielectric or semiconductor substrate because such material is relatively easy to pattern to form the raised members, as well as being scalable to relatively smaller geometries and compared to other materials used in etching procedures or micromachining operations.
Optionally, one or more projecting apex structures are formed in top surface of the raised member, upon which is positioned the conductive layer opposite the top surface of the raised member. The projecting apex structures facilitate the establishment of ohmic contact with the leads by penetrating the surface of the leads, including any oxide layer that may have been formed thereon.
According to a second embodiment of the invention, an interposer is provided, wherein the raised members are replaced with an array of depressions formed into the dielectric or semiconductor substrate. A conductive layer is deposited or otherwise formed on an inside surface of each of the depressions. The depressions are aligned and spaced so that the leads of an integrated circuit package may be placed therein and become electrically engaged with the conductive layers. For example, the depressions may take the form of trenches, each having a longitudinal axis parallel to the longitudinal axis of the corresponding lead. The trenches or other depressions may have one end that is open into a nest or other low elevation region on the face of the interposer structure. The nest may facilitate placement of the leads into the depressions by allowing the integrated circuit package to rest low on the interposer and near to the plane defined by the array of depressions.
According to either of the foregoing embodiments, electrical traces preferably extend from the conductive layer along a surface of the body of the interposer structure. The traces preferably have a contact pad at one end thereof where a conductive structure such as a wire or conductive tape may be attached. Any suitable conductive structure may be used to electrically connect the trace with external circuitry, such as that found in a testing apparatus. For example, conductive tape may be attached to the leads to provide an electrical path to the testing device. According to a preferred configuration of the interposer structure, the conductive tape wraps around an edge of the interposer structure and extends to a face of the interposer structure opposite the contact structures. The conductive tape may end at a terminal contact point that can be connected to a conventional socket or probe. Preferably, the terminal contact points on the conductive tape are not aligned across the surface of interposer structure, but are instead staggered, thereby increasing the distance between adjacent terminal contact points and increasing the pitch.
When an integrated circuit package is electrically connected to the interposer structure, the integrated circuit package may advantageously be secured thereover in order to reliably establish electrical connection. This can be accomplished by any of a number of suitable methods. For example, a clamping apparatus may be brought into contact with the leads or with another part of the integrated circuit package. The clamping apparatus may be a bar or a plate that is pressed onto the integrated circuit package on the opposite side thereof from the interposer structure. Alternatively, a vacuum source may be connected to a via that extends through the interposer structure and terminates at an end that is adjacent a portion of the body of the integrated circuit package. Using the vacuum source, the integrated circuit package may be held onto the interposer structure by differences in air pressure. In any case, when the interposer structure is used for testing an integrated circuit, the method of securing the integrated circuit package onto the interposer structure is preferably temporary.
According to still another embodiment of the invention, the raised members and depressions of the previous embodiments are replaced with an array of conductive bumps. The interposer structure of this embodiment includes a substrate over which a plurality of segments of conductive tape are positioned. A conductive bump is deposited over each segment of conductive tape in order to provide contact surfaces for electrically engaging the leads of the integrated circuit package.
In view of the foregoing, the interposer structures of the invention are able to establish electrical connection to leads relatively near the body of an integrated circuit package. This is possible even in situations where the leads have a very fine pitch. Moreover, reliable temporary electrical contact with leads can be established without damaging the leads.